In order to keep damage-related downtimes of machine tools to a minimum, it is important to keep various spare parts in stock. This is particularly important for highly complex components such as the motor spindle, but it is not easy. It should also be borne in mind that not every machine is equally important for a manufacturing company. Weiss Spindeltechnologie from Maroldsweisach therefore offers a step-by-step model for restoring its spindles, which differs primarily in terms of provisioning time. In the simplest case, the procurement of damaged parts is only initiated when required. Damage can be repaired much more quickly if the most important repair parts or even complete replacement spindles are stored - for example in the Weiss spindle pool.

As an alternative to complete replacement spindles, Weiss also stocks the most important repair parts for customers and installs them as required. (Image: Weiss)

This is because there are many criteria that need to be considered when it comes to bearings to ensure that the spindle functions reliably in an emergency. The roller bearings used require particular attention. Without appropriate care, there are problems with steel bearings in particular, as Weiss Sales and Service Manager Christian Kleinhenz explains: "It is crucial that the bearings are spring preloaded. This means that the lubricant is pressed out between the raceway and the rolling element, creating two elliptical contact surfaces per rolling element. If the bearing rings and rolling elements are made of steel, corrosion can form over time. This happens more frequently if the spindle is exposed to vibrations at the bearing location. This is not uncommon, especially in production plants." The spindle must therefore be mounted with low vibration. In addition, the rolling elements must be moved regularly to shift the contact surfaces.

Move bearing grease regularly

If spindles are not moved, standstill marks can form on rolling bearings. Regular grease distribution runs ensure that the rolling bearings of the spindles retain their lubricating and sliding properties. During this process, the specialists at Weiss also determine the relevant bearing condition parameters. (Image: Weiss)

Another potential danger comes from rolling bearing grease. This is not about the chemical ageing process. "This only has an effect in periods of between three and five years," says Kleinhenz: "This factor is therefore not particularly critical." The situation is different with the oil conductivity of the lubricant. You need to know how grease is structured and how it "works": around 80 percent of it consists of oil, which is contained in a soap structure. If the grease is not moved, the ability to transfer the oil from the grease reservoir to the actual contact zone suffers. As a result, the oil film between the rolling element and the bearing ring may be too thin when in use, which ultimately leads to mixed friction and wear.

As the greases used in roller bearings can only be refreshed using very complex and cost-intensive processes, it is important to prevent them from losing their central lubricating and sliding properties. Weiss ensures this by subjecting the spindle to so-called grease distribution runs at the technically necessary intervals. "Although oil-air lubricated spindles do not have this disadvantage by definition, regular inspections are advisable here too," adds the service manager. During these processes, the specialists collect current measurement data and compare it with the data recorded during the original acceptance test. If the rolling bearing condition parameters match, the spindle is returned to storage, otherwise the rolling bearings are replaced.

To ensure that the motor spindles are ready for use at all times, Weiss also inspects all other relevant functional properties as part of the recurring acceptance tests. For particularly long storage periods, all elastomer components such as seals are also checked. In this way, Weiss keeps the replacement spindles stored in the pool functional and ready for use at all times. If a customer finally requests them, they are delivered in the shortest possible time - depending on the agreement. As the Siemens subsidiary is internationally positioned, customer spindles can be stored at numerous supra-regional locations. This means that delivery times can usually be kept very short. as